1. Field of the Invention
The present invention relates to a recording apparatus and method configured to record an image by applying a recording agent to a recording medium.
2. Description of the Related Art
Recently, OA apparatuses, such as personal computers and word processors, have been in widespread use. Various recording apparatuses configured to record information, which is outputted from the OA apparatuses, onto various recording media have been provided. Especially, inkjet recording apparatuses have gained widespread acceptance by users due to various advantages, such as low noise, low running cost, compact size, and relative ease of colorization. There have been recently increased demands for outputting images, which are taken by digital cameras, with quality as high as that of silver-halide photographs. To fulfill the demands, diverse recording methods employing various ingenuities have been implemented. For example, at a front or rear end portion of a recording medium, accuracy in conveying a recording medium tends to be reduced due to the structures of recording apparatuses. To address this problem, some inkjet recording apparatuses have already been provided, which employ special recording methods to record images on front or rear end portion of a recording medium.
Hereinafter, practical problems relating to the “recording of an image on a front or rear end portion” are briefly described.
Regarding recording of an image on a front or rear end portion, an image is liable to be distorted when the image is recorded on the front end portion or the rear end portion of a recording medium. A major cause of this tendency is that the recording medium comes off a part of pairs of rollers, which support the recording medium from both upstream and downstream sides thereof and convey the recording medium. This state is described in detail hereinbelow with reference to the accompanying drawings.
FIG. 1 is a schematic view illustrating a recording head, which records an image on a central portion of a recording medium, and a conveying mechanism that conveys the recording medium P while supporting the recording medium P. As shown in FIG. 1, a conveying roller M3060 and two paper discharge rollers M3100 and M3110 are opposed to and are engaged with a pinch roller M3070, and spurs M3120, respectively, to thereby form three nip units that stretch and support the recording medium P. The three pairs of the rollers rotate to thereby enable conveyance of the recording medium P in a direction indicated by an arrow shown in FIG. 1.
Reference character H1000 designates ahead cartridge, in which a plurality of recording elements (or nozzles) operative to discharge ink is arranged at predetermined pitches in the conveying direction shown in FIG. 1. Ink is discharged from each of the recording elements while the head cartridge H1000 scans in a front-to-back direction perpendicular to the plane of the drawing of FIG. 1. Thus, an image is formed on an area of the recording medium P, which is placed between the conveying roller M3060 and the discharge roller M3100. Such a recording scanning operation by the head cartridge H1000, and an operation of conveying the recording medium P by the three pairs of the rollers are alternately repeated, so that images are sequentially formed on the recording medium P.
FIG. 2 shows a state in which the recording of images is progressed from a state shown in FIG. 1 and in which the recording of images is being performed on the vicinity of a rear end portion of the recording medium P. The recording medium P has already come off the conveying roller M3060 and is conveyed only by the rotation of the discharge rollers M3100 and M3110.
Meanwhile, generally, it is frequent that the differences in the main roles among the conveying roller M3060 and the discharge rollers M3100 and M3110 cause the slight differences in roller-diameter and conveying-accuracy thereamong. The major role of the conveying roller M3060 is to position the recording medium at an appropriate place with respect to the recording head in each recording scan. Thus, the conveying roller M3060 has a sufficient roller diameter and can perform the conveying operation with desired accuracy. On the other hand, the major role of each of the discharge rollers M3100 and M3110 is to reliably discharge the recorded recording medium. Thus, usually, the discharge rollers M3100 and 3110 are smaller in roller-diameter than and are inferior in accuracy of conveying the recording medium to the conveying roller M3060. That is, the accuracy in conveying an area to be conveyed between a moment at which the rear end portion of the recording medium P comes off the conveying roller M3060 and a moment at which the recording of an image on the rearmost end of the recording medium P is terminated is reduced as compared with the accuracy in conveying precedent areas of the recording medium P. At that time, in some recorded images, black streaks are confirmed in a case where an amount of the conveyed area is in sufficient. Conversely, white streaks are confirmed in a case where the amount of the conveyed area is too large. Thus, there is a fear that the streaks may be non-negligible deterioration of image quality.
Also, deterioration of image quality is caused due to the fact that both end portions of the recording medium are not held. When the rear end portion of the recording medium P comes off the conveying roller M3060, the distance (hereunder referred to as “a head-paper distance”) between the recording head and the recording medium varies to no small extent. Thereafter, the head-paper distance is unstable yet. The inkjet recording head moves while discharges ink with timing determined according to a predetermined “head-paper” distance maintained by the rollers of the pairs respectively placed ahead and behind the head. Then, ink discharged with appropriate timing becomes dots on the recording medium, which are arranged at appropriate pitches, to thereby form an image. Thus, when the head-paper distance is changed during recording, or when the head-paper distance largely varies, the positions of the dots on the recording medium become unstable, so that deterioration of image quality, such as white streaks, black streaks, and textured images, may occur. The problem with the head-paper distance occurs not only in the case of recording an image on the rear end portion of the recording medium but in the case of recording an image on the front end portion thereof.
FIG. 3 is a view showing a state in which an image is recorded on the vicinity of the front end portion of the recording medium P. The recording medium P is held and conveyed only by the conveying roller M3060. In the case of recording an image on the front end portion, the conveyance of the recording medium P is performed by the conveying roller M3060 instead of the discharge rollers M3100 and M3110. Thus, the conveyance of the recording medium P is performed with higher accuracy, as compared with the state in which an image is recorded on the vicinity of the rear end portion, which is described by referring to FIG. 2. However, the head-paper distance problem is caused due to the fact the front end of the recording medium is not held, similarly to the case of the state shown in FIG. 2. That is, the positional accuracy of the dots on the recording medium is unstable, as compared with that in the case of recording an image on a central portion of the recording medium.
To address the aforementioned problem of recording images on the front end portion and the rear end portion of the recording medium, a serial type recording apparatus employs a method of suppressing a recording width (that is, the number of recording elements actually discharging ink) of the recording head only when images are recorded on the front end portion and the rear end portion of the recording medium, and of reducing an amount of a conveyed recording medium in response thereto (see, for example, Japanese Patent Application Laid-Open No. 2004-98668). Reducing the recording width of the recording head can suppress the variation in the head-paper distance with respect to the recording width. In this case, this recording apparatus exerts the effects of suppressing textured images generated, especially, when performing multi-pass recording, which will be described later. Even when the conveying accuracy is reduced, a conveying error can be decreased by reducing the amount of the conveyed recording medium. Additionally, the pitches at which ink is discharged onto a connecting part are reduced. Thus, this recording apparatus has the effect of obscuring white streaks and black streaks.
Also, a method of suppressing the number of recording elements, which actually discharge ink, only when recording an image on the front end portion and the rear end portion of the recording medium, and of adjusting the amount of the conveyed recording medium in response thereto is employed even in an inkjet recording apparatus employing an interlace recording method. In the interlace recording method, a recording head whose recording-element arrangement density is lower than a recording density is used, and the recording of an image is completed with a plurality of recording scans while interpolating the recording density in a subscanning direction (see, for instance, Japanese Patent Application Laid-Open No. 11-291506).
However, according to the conventional recording method, in a case where the number of nozzles used to record an image on the front or rear end portion of the recording medium is reduced, as compared with that of nozzles used to record an image on the central portion of the recording medium, the rate of the number of the reduced nozzles is set to be constant, regardless of recording modes. That is, even in a high-speed mode, the number of used nozzles is limited to be about equal to that of nozzles used in a high-quality mode. Consequently, a recording time needed to record an image on the front or rear portion is relatively long.